Characterization of light toxicity on retinal ganglion cells in vivo and in vitro

Abstract

Purpose: Light has not yet been identified as a risk factor in retinal diseases involving retinal ganglion cell degeneration such as glaucoma or diabetic retinopathy. Recently, we showed that retinal ganglion cells (RGCs) degenerate in taurine-depleted animals, in which a light-dependent degeneration of photoreceptors had previously been shown in the 70-80s. Here, we tested if RGCs are preserved in taurine-depleted mice maintained in darkness. In vitro, we characterized the most phototoxic wavelengths for purified retinal ganglion cells in culture using our specific cell illumination device within the blue-green range, which has already enabled us to define the spectral band from 415 to 455 nm as the most toxic for A2E-loaded RPE cells.

Methods: For in vivo experiments, mice were treated for 2 months with GES, a taurine transporter blocker and maintained or not in darkness. Retinal cells density was then quantified on sections following immunolabeling. To identify the most toxic wavelengths, purified rat RGCs were exposed to 10 nm illumination bands centered from 390 to 520 nm in 10 nm increments for 15 hours. Light irradiances were normalized with respect to the natural sunlight reaching the retina after ocular media filtering. Control cells were maintained in darkness during the experiment. Cell viability was assessed using CellTiter-Glo Assay (Promega).

Results: GES-treated mice showed a significant reduction in the densities of both cone photoreceptors and RGCs. The RGC cell loss did not appear as a secondary process to the cone degeneration because these degenerative processes were occurring at the same rate. Degeneration of both RGC and cone was not detected in GES-treated animals maintained in darkness. Following this in vivo demonstration of toxicity of light on RGCs, we defined the phototoxic action spectrum on purified RGCs. After light exposure, morphological changes were associated with a loss of cell viability. Quantification of viable cells revealed that the RGC phototoxicity was significantly higher in a 60 nm spectral band centered at 460 nm.

Conclusions: These results demonstrated for the first time light effect on RGC degeneration in vivo. Furthermore, the in vitro study suggests that blue light is more toxic to RGCs. Interestingly, this RGC phototoxicity action spectrum is at higher blue wavelengths compared to the RPE action spectrum that we have previously reported on A2E-loaded RPE cells.

Keywords: 531 ganglion cells • 670 radiation damage: light/UV • 695 retinal degenerations: cell biology